1. Field of the Invention
The present invention refers to the field of preparing coffee by means of a coffee machine which is supplied with water and coffee beans. More specifically, the invention refers to a process for the proportioning of coffee powder in a coffee machine as well as to an apparatus for performing said process including a coffee machine equipped with a grinding mill adapted to prepare the required coffee powder from the coffee beans and with a processing chamber receiving the proportioned coffee powder to be brewed in order to furnish the desired coffee.
2. Prior Art
Known coffee machines of this kind contain a grinding mill driven to a constant speed by means of an electric motor. At the outlet aperture of the grinding mill, the milled coffee prepared by the grinding mill falls into a processing chamber, where it is subsequently brewed by means of hot water or steam. The proportioning of the amount of coffee powder, which is to be filled into the processing chamber, is performed in the known coffee machines by a time control means, inasmuch as the duration of the operation of the grinding mill driving motor is controlled. Under the already mentioned assumption that the motor is driven to a constant speed, the amount of coffee powder falling into the processing chamber may thereby be proportioned by means of a variation of the operating time of the motor.
In the case of bigger coffee machines, as being used, e.g. in restaurants, such equipment works substantially satisfactorily. The most important factor inhibiting a transformation of this concept to household coffee machines is the expensive motor for the grinding mill, which is usually an induction motor.
In the past, one has tried to solve this problem by providing a proportioning chamber adjoining the outlet of the grinding mill. As soon as said proportioning chamber is filled with coffee powder provided by the mill, the chamber is opened and its content is supplied to the processing chamber of the coffee machine. An apparatus of this kind is disclosed e.g. in the German Patent Publication No. 28 47 220. Thereby the coffee powder is thrown into the proportioning chamber, which is in a closed position, by means of an arrangement including a plurality of bars, levers and springs. As soon as the chamber is filled with coffee powder, the pressure of the powder should act on the walls of the proportioning chamber. One wall portion thereof is now intended, under the influence of said pressure, to pivot downwardly and releases a lever which, amongst else, disengages the clutch driving the grinding mill. Such a construction seems not only to be very complicated and thereby very expensive in view of the plurality of mechanical elements required for a proper operation, but it must also be assumed that the reliability and the precision of the proportioning process will be degraded during its operation time since these mechanical elements are subjected to considerable wear.